Traditional fabrics have, for centuries, been decorated and had their surface texture modified by embroidery and other needle arts. Originally, this process was obtained through tedious hand labor, painstakingly applying fine stitches that had the cumulative effect of building up a region of the background fabric according to some particular pattern. The resulting product had a base fabric, comprised of threads or yarns, woven or knitted according to some pattern, a raised region formed by a collection of threads in some stitch pattern, and an overall pattern of these raised regions determined by their respective size, shape, orientation and placement. While rich in appearance, these products were complicated to create and costly to produce.
Most nonwoven fabrics are flat and visually uninteresting In some instances, nonwoven fabrics are embossed or printed with some sort of design to provide visual interest. In other instances, nonwoven fabrics are provided with an integral pattern during the course of their manufacture. Those having an integral pattern of their own fall into two categories:
1) Apertured fabrics--where a pattern is created by a network of bundled fiber segments surrounding apertures or holes; or PA1 2) Weight patterned fabrics--fabrics that achieve a visual effect by concentrating fibers into regions of higher basis weight to increase opacity relative to the lower basis weight regions which are more translucent.
It is important to differentiate between basis weight and density. "Basis weight" is the weight of a unit area of fibrous web or fabric or portion thereof being characterized. Basis weight has also been called "area density" in some prior art patents. The term "density" is the weight of a unit volume of a fibrous web or fabric or portion thereof being characterized. "Density" has also been called "volume density" in some prior art patents. Typical embossing processes create regions of higher density without altering the basis weight. Traditional nonwoven patterning processes produce regions of varying basis weights while maintaining substantially uniform density.
The prior art nonwoven fabrics made with these known patterning processes do not have clear, well defined raised portions and therefore the desired patterns are difficult to see. In addition, the raised portions of prior art embossed nonwoven fabrics are not dimensionally stable and their raised portions lose their three-dimensional structure when stressed, as for example, when they are handled or laundered.
Processes for making nonwoven fabrics have been known for many years. In one process, a fiber batt or web is treated with water streams to cause the fiber to entangle with each other and provide some strength in the batt. Many methods have been developed for treating fiber batts in this manner in an attempt to duplicate the physical properties and appearance of woven fabrics.
U.S. Pat. Nos. 5,098,764 and 5,244,711 disclose the use of a support member in one such method of producing nonwoven fabrics. The support members have a topographical feature configuration as well as an array of apertures. In this process, a starting web of fiber is positioned on the topographical support members. The support member with the fibrous web thereon is passed under jets of high pressure fluid, typically water. The jets of water cause the fiber to intertwine and interentangle with each other in a particular pattern, based on the topographical configuration of the support member.
The pattern of topographical features and apertures in the support member is critical to the structure of the resulting nonwoven fabric. In addition, the support member must have sufficient structural integrity and strength to support a fibrous web while fluid jets rearrange the fibers and entangle them in their new arrangement to provide a stable fabric. The support member must not under go any substantial distortion under the force of the fluid jets. Also, the support member must have means for removing the relatively large volumes of entangling fluid so as to prevent "flooding" of the fibrous web, which would interfere with effective entangling. Typically, the support member includes drainage apertures which must be of a sufficiently small size to maintain the integrity of the fibrous web and prevent the loss of fiber through the forming surface. In addition, the support member should be substantially free of burrs, hooks or the like irregularities that could interfere with the removal therefrom of the entangled fabric. At the same time, the support member must be such that fibers of the fibrous web being processed thereon are not washed away under the influence of the fluid jets.